Wooden beams with sections that are subjected to transversal tension

ABSTRACT

A wooden beam ( 1 ) has several sections which are subjected to a transversal tension and which affect in particular the areas in which there are recesses or openings ( 3 ). Rod-shaped elements are provided in the form of screws ( 4 ) which are introduced in such a way that they extend crosswise to the longitudinal direction of the beam ( 1 ) in order to absorb this transversal tension. These screws are screwed in from the top side ( 5 ) or the underside ( 6 ) of the beam ( 1 ) and each extend over part of the height (H) of the beam ( 1 ) only and are therefore directly associated with the area ( 2 ) that is subjected to transversal tension.

The invention relates to a wooden beam having sections which aresubjected to transverse tension, which are reinforced by rod-shapedelements which are positioned to extend essentially transversely to itslongitudinal direction.

Especially at through-holes in the span of such wooden beams, or else inthe vicinity of their ends, if cut-outs are provided in the vicinity ofthe superposition region, there arise exceptional stresses due to forceswhich act transversely to the grain orientation, so that in those areastears and cracks can form in the wooden beam parallel to the grainorientation.

It has already been proposed to insert, precisely in those sections ofwooden beams subjected to transverse tension, rod-shaped elements forspecial reinforcement. In general, these rod-shaped elements were gluedinto pre-drilled holes. This yielded a certain amount of beamstrengthening transversely to its longitudinal direction, i.e.transversely to the grain orientation.

In this regard, the premise is that the drill holes provided for theinsertion of the rod-shaped elements heretofore normally extended overthe entire height of a beam, or were provided at least starting at thetop or at the bottom of the beam until well beyond the section that wasactually subjected to transverse tension. On the one hand, this causes acorresponding consumption of time for creating the drill hole, forinserting the rod-shaped element and for gluing it in, and on the otherhand, there results an exceptional consumption of materials throughcorrespondingly long rod-shaped elements and a correspondingly largerequired quantity of adhesive.

The present invention has as its objective to substantially improve thereinforcement possibilities for a beam of the initially describedvariety in the region of sections subjected to transverse tension.

This is accomplished in accordance with the invention by forming therod-shaped elements of screws which are provided with threaded segmentsat both of their end regions, which extend over a zone subjected totransverse tension, which are screwed in from the top or the bottom ofthe beam, which extend only over a portion of the height of the beam andwhich are therefore associated directly with the zone that is subjectedto transverse tension.

Through these inventive measures, it has become possible to utilizerelatively short screws instead of the prior, very long rod-shapedelements. Absorption of the tension forces is carried out solely by thethreaded portions, which are engaged in the wood of the beam.

By means of the invention, there has been created the possibility, inpractice, to utilize a screw for the present purpose, which is insertedappropriately deeply and is therefore located where correspondingtransverse tension forces occur. This is advantageous especially forexceptionally tall wood beams. Such beams can have a height of one meteror more, but reinforcement due to the prevailing transverse tension isneeded only over a predetermined segment of the beam height.

A preferred embodiment is one in which the screws extend approximatelyequally far above and below a zone of increased transverse tension. Thisensures that the thread portions which are present at both ends of thescrew provide adequate anchoring to essentially equal degrees, so thatthe transverse tension forces can be absorbed without any problems.However, such an arrangement becomes possible only if the screws can bescrewed into the wooden beam less deeply or even more deeply, asappropriate.

In this connection, it is preferred that the length of the screws bechosen shorter than one half the height of the beam. Especially forbeams of exceptional height this yields a very substantial saving ofmaterial and furthermore, especially when using screws with threadedsections, there occurs the lowest possible insertion turning moment.Such screws can be screwed into the wood beam without predrilling ahole, which also makes possible an appropriately deep insertion.

Especially in a wood beam of relatively great height, there occur incertain regions—for example in the middle region of a curvedbeam—several sections subjected to transverse tension, and this canaffect layers in all regions relative to the height of the beam. In sucha case, the inventive technique can also be used advantageously, namelyby screwing into sections subjected to transverse tension two or morescrews spaced apart and approximately parallel to each other and axiallydisplaced over the height of the beam. Thus, a relatively large segmentof a beam can be provided with exceptional transverse tensionreinforcement, namely through the screwing in of a multiplicity ofscrews which are screwed in from the top or the bottom side of the beamand in so doing are screwed in more or less far.

A preferred embodiment provides that the screws are equipped with athread over their entire shaft length. This ensures that the screws canengage the wood of the beam over their whole length and are thereforecapable of absorbing relatively high transverse tension forces.

It is further proposed that the screws have an internal tool drive attheir one end, with the diameter of the segment of the screws whichsurrounds this internal tool drive being made approximately equal to oronly slightly greater than the outer diameter of the thread. In thisway, it becomes possible to screw the screw in relatively deeply withoutsignificant increase of the screwing-in moment and without damage to thethreaded region inside the wood. In this way, it also becomes possibleto screw the screws in very deeply so as to bring them to just thatpoint where the sections subjected to transverse tension are present.

A preferred and very simple procedure for screwing the screws into thewood beam exists if the screws are screwed in with a screwdriver bithaving a shaft adjoining the screw-engaging region, or an imaginarycylinder enclosing the shaft, which has a diameter that is equal to orsmaller than the diameter of the portion of the screw which surroundsthe internal tool drive and which has a length sufficient to bridge theregion of the height of the beam from the internal tool drive of thescrew all the way to the upper or lower limit, and beyond to thescrewdriver engagement point. Thus, by use of a relatively longscrewdriver bit the screws can be screwed to the desired depth into thewood beam. Without requiring pre-drilling, there is therefore createdthe possibility to place the screw at the appropriate location relativeto the height of the beam.

Additional inventive characteristics and special advantages aredescribed further in the following description with reference to thedrawings. There is shown by:

FIG. 1 a segment of a curved wood beam in cross-section, illustratingdifferent segments subjected to transverse tension;

FIG. 2 an enlarged illustration of a section from the beam according toFIG. 1 and illustrating a through-hole;

FIG. 3 an enlarged illustration of an end region of a beam having anotch;

FIG. 4 to FIG. 8 various embodiments and portions of wood beams, inparticular showing sections subjected to transverse tension.

In a wood beam 1 there exists a series of zones 2 subjected totransverse tension, which extend substantially in the lengthwisedirection of the beam 1, i.e. in the grain orientation of the wood.Whether the entire cross-section of this beam is formed of solid wood orof laminated wood, i.e. as a glued laminate, has practically noinfluence upon the behavior of sections subjected to transverse tension,because transverse tension is always present in the region of cutouts orthrough-holes 3 as well as in other regions.

In place of the previously common techniques (pre-drilling—insertion ofrod-shaped elements—gluing-in of these rod-shaped elements—relativelylong drying period for the adhesive) a screw 4 is now to be screweddirectly into the entire material of beam 1. These screws 4 which are tobe used here have threaded segments at least at both of their endregions. However, it is also possible to provide a thread over theentire shaft length of the screws 4. For beams 1 of relatively greatheight H the length L of the screws 4 is less than one half the height Hof the beam 1.

For beams of lesser height H, this relationship to the length L of thescrews 4 can also proceed in the opposite sense. Only as an example, itcan be stated that for a beam height H of one meter a length L of 20 cmor less can be used for screws 4.

This is possible especially because the screws 4 are placed precisely atthe zone subjected to transverse tension. After screws 4 are screwed infrom the top side 5 or from the bottom side 6 of the beam 1, the screws4 are screwed in so far that they are located immediately adjacent tothe zone 2 subjected to transverse tension. From FIGS. 1 to 3 it canalso be seen that the screws 4 preferably extend approximately equallyfar above and below such a zone 2. This enables optimum absorption ofthe transverse tension forces by the regions of beam 1 adjacent to therespective zones 2.

Especially in the illustration of FIG. 1 (example all the way to theright) it is shown that in the segments subjected to transverse tensionseveral zones are distributed over the height H of beam 1 which aresubjected to transverse tension. Into these sections there can bescrewed in two or more screws 4 spaced apart and oriented approximatelyparallel to each other, with these being screwed in axially, i.e.displaced from each other over the height H of beam 1.

Within the scope of the invention it is also possible to screw in two,or more than two screws 4 immediately behind each other co-axially, inwhich case the first screw must be sunk in sufficiently deeply. In sucha case, the next following screw can optionally have a larger outerdiameter. Screws 4 can also be screwed in co-axially from oppositesides, i.e. from the topside 5 and bottomside 6 of beam 1, if the screwsare to extend over a correspondingly larger region of the height H ofbeam 1.

The screws have an internal tool drive at one of their ends, thediameter of the section of screws 4 which surrounds the internal tooldrive being as large as, or only slightly larger than the outer diameterof the thread. This makes possible relatively easy screwing in of screws4 into this relatively deeply sunk in position since the large “head” ofthe screw does not create a significant increase in turning momentduring screwing in of screws 4.

The screwing in of screws 4 into this relatively deeply sunk-in positioncan be accomplished in simple manner with an appropriate screwdriver bitwhose shaft adjoining the engagement region for applying to the screw,or an imaginary cylinder enclosing the shaft, has a diameter which isequal to or smaller than the diameter of the section of screw 4surrounding the internal tool drive. This screwdriver bit is long enoughto bridge the portion of the beam height H from the internal tool driveof screw 4 to the upper or lower limit 5 or 6 of the beam 1, and beyondto the screwdriver engagement point. In this connection, it is alsopossible to provide, for example on the screwdriver bit, appropriatemarkings in order to be able to precisely determine into whichscrewed-in depth in beam 1 the screw 4 has been driven. Thus thescrewdriver bit could be provided, for example, with indentations, colormarkings or the like.

Depending upon the particular area of application of screws 4, i.e.depending upon the configuration and shape of the through-holes in abeam 1, depending upon its curvature or upon its span width, sectionssubjected to transverse tension also occur at various segments of thebeam 1 and therefore also very specific zones 2 subjected to transversetension. For example, from FIG. 4 it can be seen that such zones 2subjected to transverse tension exist in the middle region of the lengthof curved beams 1. Likewise, such zones 2 subjected to transversetension occur in beams which exhibit a kind of roof shape on their uppersides. Here, too, transverse tension forces occur in practice in themiddle region relative to the overall length of the beam. From FIG. 6 itcan be seen that for a through-hole 3 the zones which are subjected totransverse tension are not necessarily present at different heights onboth sides of this through-hole 3, but can also be experienced at thesame height. This is appropriately determined as a function of theloading of a wooden beam.

Zones 2 subjected to transverse tension also occur at a U-shaped notchin a beam 1, for insertion of a transversely extending girder 7. In theembodiment of FIG. 8 there is illustrated an addition to the arrangementencountered in practice, which is also illustrated in FIG. 3. At acorresponding notch 8 in wooden beam 1, there also occurs, right in theillustrated region, a zone 2 which is subjected to transverse tension.

In all of these sections subjected to transverse tension, and especiallyin the specific zones 2 subjected to transverse tension, the use inaccordance with the invention of screws which are screwed in directly,i.e. without predrilling, appropriate transverse stress reinforcementcan be achieved.

What is claimed is:
 1. A wooden beam comprising sections subjected totransverse tension which are reinforced by rod-shaped elements whichextend substantially transversly to the longitudinal direction thereof,the rod-shaped elements are formed by screws (4) provided at least inboth their end portions with threaded segments having threads, whichextend across a zone (2) subjected to increased transverse tension andare screwed in from the top or the bottom side of the beam (1), extendover only a portion of a height (H) of the beam, a length (L) of thescrews (4) being less than one-half the height (H) of the beam (1), andthus are associated directly with the zone (2) subjected to increasedtransverse tension.
 2. A beam according to claim 1, characterized inthat the screws (4) extend approximately equally far above and belowsaid zone (2) subjected to increased transverse tension.
 3. A beamaccording to claim 1, characterized in that in sections subjected totransverse tension, two or more screws (4) are screwed in spaced-apartand oriented approximately parallel to each other and displaced axiallyfrom each other over the height (H) of the beam (1).
 4. A beam accordingto claim 1, characterized in that the screws (4) are provided with athread along an entire shaft length.
 5. A beam according to claim 1,characterized in that the screws (4) have at one end an internal tooldrive, a diameter of the portion of the screws (4) surrounding theinternal tool drive being approximately as large or only slightly largerthan the an diameter of the thread.
 6. A beam according to claim 1,characterized in that the screws (4) are screwed in with a screwdriverbit having a shaft adjoining an engagement region for applying to thescrew (4), or an imaginary cylinder enclosing the shaft, which has adiameter which is equal to or smaller than a diameter of a portion ofscrew (4) which surrounds the internal tool drive and has a length whichbridges a portion of the height (H) of the beam (1) from the internaltool drive of screw (4) to an upper or lower limit (5, 6), and beyond tothe screwdriver engagement point.
 7. A beam according to claim 1,wherein said zone (2) is a through-hole or cutout in the beam.
 8. A beamaccording to claim 7, wherein said zone (2) includes a crack in saidbeam extending from said through-hole or cutout.